1) Field of the Invention
This invention relates generally to fabrication of magnetoresistive (MR) sensors employed within data storage and retrieval. More particularly, the present invention related to enhanced magnetoresistive (MR) spin valve filtering giant magnetoresistance (GMR) sensor elements.
2) Description of the Prior Art
In recent years, improvement in sensitivity of magnetic sensors and increase in density of magnetic recording are advancing. Concomitantly, development of magnetoresistance effect magnetic sensors (hereinafter abbreviated to MR sensors) and magnetoresistance effect magnetic heads (hereinafter abbreviated to MR heads) is making rapid progress. Each of the MR sensors and the MR heads is operable to read an external magnetic field signal as an electric resistance variation in a sensor in response to the external magnetic field. In these MR sensors and MR heads, reproduction outputs do not depend upon relative speeds with respect to recording media. This leads to high sensitivity of the MR sensors and high output levels of the MR head in high-density magnetic recording.
Recently, proposal is made of a magnetoresistance effect film which comprises at least two ferromagnetic layers or thin films stacked one over the other with a nonmagnetic layer or thin film interposed therebetween, and an antiferromagnetic layer or thin film underlying a first one of the ferromagnetic thin films so that the first ferromagnetic thin film is provided with antimagnetic force, that is, constrained by exchange anisotropy or exchange biasing.
A so-called soft magnetic material or a high permeability magnetic material is usually used for the ferromagnetic layers. The term xe2x80x9cnonmagneticxe2x80x9d is usually used to mean xe2x80x9cparamagneticxe2x80x9d and/or xe2x80x9cdiamagneticxe2x80x9d.
When an external magnetic field is applied to the magnetoresistance effect film, the direction of magnetization of the other second one of the ferromagnetic thin films is rotated with respect to that of the first ferromagnetic film. Thus, change in resistance takes place.
Disclosure is also made of a conventional magnetic read transducer, called an MR sensor or an MR head, which can read data from a magnetic surface with high linear density. The MR sensor detects a magnetic field signal through change in resistance as a function of the intensity and the direction of magnetic flux detected by a reading element. The above-mentioned conventional MR sensor is operated on the basis of an anisotropic magnetoresistance (AMR) effect. Specifically, one component of the resistance of the reading element changes in proportion to the square of the cosine of the angle between the magnetization direction and the direction of the sense current flowing through the element.
More recently, disclosure is made of a further remarkable magnetoresistance effect. Specifically, change in resistance of a stacked-type magnetic sensor results from spin-dependent transmission of conduction electrons between ferromagnetic layers with a nonmagnetic layer interposed therebetween and from interfacial spin-dependent scattering accompanying the spin-dependent transmission. Such magnetoresistance effect is called by various names such as xe2x80x9ca giant magnetoresistance effectxe2x80x9d and xe2x80x9ca spin-valve effectxe2x80x9d. Such magnetoresistance effect sensor made of an appropriate material has improved sensitivity and exhibits large rate of change in resistance. In the MR sensor of the type described, in-plane resistance between a pair of the ferromagnetic layers separated by the nonmagnetic layer changes in proportion to the cosine of the angle between magnetization directions in the two ferromagnetic layers.
It has been recognized that the electronic and structural natures of interfaces are key elements in the understanding of mechanism behind GMR effects. Improved electron reflectivity in the GMR/Insulator interface was found to improve significantly the GMR ratio.
There is a need to improve the electron reflectivity in the GMR/Insulator interface. This invention is directed towards this end.
The importance of overcoming the various deficiencies noted above is evidenced by the extensive technological development directed to the subject, as documented by the relevant patent technical literature. The closest and apparently more relevant technical developments in the patent literature can be gleaned by considering U.S. Pat. No. 5,943,589(Hoshiya et al.) and U.S. Pat. No. 5,766,743(Fujikata et al.).
It is an object of the present invention to provide a method for fabricating a giant magnetoresistance (GMR) with an enhanced spin filtering.
It is an object of the present invention to provide a structure for a spin filtering GMR configuration with an enhanced signal amplitude.
It is towards the forgoing objectives and other objective apparent in the specification below that the invention is directed.
The GMR configuration of the invention, in the first embodiment (a SVGMR), has an important buffer layer 13 composed of an metal oxide having a crystal lattice constant that is close the 1st FM free layer""s crystal lattice constant and has the same crystal structure (e.g., FCC, BCC, etc.). This metal oxide under layer replaces the Ta conductor used in the inventor""s previous process. The invention""s metal oxide buffer layer enhances the specular scattering. The invention""s buffer layer is comprised of oxides of metals that have a similar crystal lattice structure and constant to the adjacent FM layer.
In the second embodiment (a spin filter -SVGMR), a high conductivity layer (HCL or filtering layer) is formed over the buffer layer. The HCL layer enhances the GMR ratio of the spin filter SVGMR. The buffer layer is a key element of the Spin filter GMR sensor of the second embodiment.
In the third embodiment of the invention, the pinned ferromagnetic layer (2nd FM pinned ) is composed of a three layer structure comprising: (a) a lower AP1 layer, a non-magnetic spacer (e.g., Ru) layer and an upper AP layer (AP2 layer) wherein the spacer layer induces anti-ferromagnetic coupling between AP1 and AP2 which enhances the pinning effect. The buffer layer 13 is present in the GMR sensor of the third embodiment.
A preferred first embodiment of the invention""s spin valve giant magnetoresistance (SVGMR) sensor comprises: a substrate; a seed layer over the substrate, the seed layer being formed of a magnetoresistive resistivity sensitivity enhancing material selected from the group consisting of nickel chromium alloys, nickel -chromium-copper alloys and nickel-iron-chromium alloys; a metal oxide layer (Buffer layer) over the seed layer; said metal oxide layer comprised of NiO (nickel oxide) or alpha Fe2O3 (alpha ferros oxide); a free ferromagnetic layer over said metal oxide layer; a non-magnetic conductor spacer layer over said free ferromagnetic layer; a pinned ferromagnetic layer (2nd FM pinned) over the non-magnetic conductor spacer layer; and a pinning material layer over the pinned ferromagnetic layer; and a capping layer over said pinning material layer.
The second embodiment of the invention is a Spin filter SVGMR that further includes: a high conductivity layer (HCL) on said metal oxide layer and said free ferromagnetic layer on said high conductivity layer (HCL). The HCL layer changes a spin valve GMR to a spin filter GMR.
A third embodiment of the invention is a pinned FM layer comprised of a three layer structure of an lower AP layer (e.g., AP1), a spacer layer (e.g., Ru) and an upper AP layer (AP2). The AP1 and AP2 layers have anti-parallel magnetic orientation. AP stands for anti-parallel.
Additional objects and advantages of the invention will be set forth in the description that follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of instrumentalities and combinations particularly pointed out in the append claims.